Large scale industrial heat sources are used for a variety of applications in industry, including sulfur recovery units, waste incinerators, and the like. Waste heat boilers are commonly used with many types of industrial heat sources to extract heat from waste gases of an industrial process to cause a component thereof to condense, or use that heat in another process or even to provide heat for the industrial facility. This is becoming increasingly important in view of global awareness of environmental preservation issues and with respect to adherence and enforcement of stricter industrial regulations, with respect to efficiency and pollution products.
An example of a waste heat boiler includes a plurality of metal boiler tubes supported by opposed metal tube sheets, as described in U.S. Pat. No. 5,954,121, the entirety of which is incorporated herein by reference. The tube sheets define a vessel for holding water or some other form of heat transfer medium. Hot waste gas passes through the boiler tubes arranged in the inlet tube sheet and heat is extracted therefrom via heat transfer from the hot gas to the heat transfer medium contained within the confines of the tube sheets. However, concerns exist with respect to compensating for the corrosive nature of the heat and gas produced by the incinerator flame, and the damage that such heat and gas can inflict on the metal components of the waste heat boiler. These concerns are addressed, for example, in U.S. Pat. No. 5,647,432, the entirety of which is also incorporated herein by reference. The '432 patent discloses refractory ferrules that are arranged to form protective wall to protect the metal components of the waste heat boiler from the corrosive nature of the incinerator heat/flame.
Improving reaction furnace efficiency is a major concern. Feed components need an adequate amount of time to fully react, and it is important to eliminate any impurities and intermediate reaction products in order to avoid undesirable reactions or other problems downstream. In addition, another concern is the prevention of corrosion of the reaction vessel and its components. Another concern exists with respect to improving the overall efficiency of the system's heat exchanging capabilities. That is, in many cases, the incinerator flame is typically not as long or wide as the vessel, and as a result, only the central tubes of the waste heat boiler effectively receive the majority of the incinerator flame, creating a hot spot at the center of the tube sheet.
In an attempt to address these concerns, one industry practice has been to implement the construction of a plurality of baffle walls between the burner and tube sheet of a waste heat boiler. These baffle walls are also provided to increase gas mixing, and thereby improve reaction efficiency. Reaction furnaces having a baffle wall construction include a plurality of spaced apart, staggered partial walls, alternately extending from opposite parts of the reaction chamber (floor and ceiling) to create a snaking gas flow therethrough over and under the alternating baffles. One problem recognized with this type of construction, however, is that dead zones are unavoidably formed behind each baffle, where no effective mixing occurs. Another problem is that baffle construction is mechanically difficult to maintain in that a plurality of partial walls extending upwardly and downwardly are not as structurally sound as a single wall traversing from top to bottom (floor to ceiling). Extra plant space, reaction furnace space, and expensive construction materials such as fire brick, etc. are required in connection with the baffle wall type construction, all which are not effectively utilized in view of the presence of the dead zones.
Another industry practice is to erect a refractory diffusor wall between the burner and tube sheet of a waste heat boiler. These diffusor walls are also referred to as checkerwalls, and have been provided to increase gas mixing, and thereby improve reaction efficiency. Checkerwalls also serve to reduce the amount of radiant heat transfer to the tube sheet, preventing thermal reactions that can physically degrade the tube sheet or lead to corrosion of the tube sheet, thereby extending the refractory life of the tube sheet, for example to achieve improved heat distribution of the incinerator flame across the entire face of the tube sheet of the waste heat boiler.
Such traditional checkerwall-type diffusor walls are typically formed of a standard-type refractory brick, typically 9″ by 2.5″ by 4.5,″ arranged in a shape of a standard wall, wherein alternating bricks are omitted to give the appearance of a checkerboard as shown in FIG. 15 (thus the name). In most cases, standard refractory brick are mortared together to define this open configuration. The typically rectangular or square holes defined by the missing bricks in the checkerwall allow the incinerator gas to pass therethrough and serve to provide a more uniform heat distribution across the entire face of the tube sheet of the waste heat boiler. However, these bricks are subject to thermal cycling, which causes the mortar to crack and fail. The overall design of traditional checkerwalls is not inherently stable, as the bricks are flat spans in constant tension, and field experience shows that this design has a tendency to fall over during a campaign.
The '121 patent discloses a different type of refractory brick particularly suited for constructing a diffusor wall (herein also referred to as a hexwall). As shown in FIG. 14, and example of such a hexwall 61 includes an array of 79 hex bricks each having a thickness of 9″ and 8″ diameter throughholes or passageways therethrough. This refractory brick is similar to that described below in connection with FIGS. 1A-1C, and includes a substantially tubular body having a passageway extending therethrough in the longitudinal direction of the body. The outer peripheral surface of the refractory brick has a complementary shape that allows for the engagement of mating means to mechanically couple a plurality of the bricks to one another, without the need for permanent adhesive, so as to cooperatively form an inherently stable diffusor wall.
In addition to offering the benefits of faster and more stable construction, without the need for mortar, another advantage of these particular hexagonal-type refractory bricks is that, when the bricks are formed in the shape of hexagons with a circular passageway formed therethrough, the open frontal area of the overall diffusor wall can reach about 50%, thereby allowing higher volume flow of exhaust gas to pass therethrough. The hexagonal bricks and the diffusor wall described in the '121 patent offer improved overall heat transfer efficiency of the waste heat boilers associated with industrial heat sources, particularly when compared to the traditional design.
It should be noted, however, that there is still a need to improve the various performance factors affecting the overall system, such as mixing efficiency, residence time, pressure drop across the system and radiant heat transfer. In addition, it would be desirable to provide simple and effective means to specifically control one or more performance factors contemporaneously in order to tailor a combination of performance factors for improved overall efficiency. No such means have been proposed heretofore.